Measuring device for contactless detecting a ferromagnetic object

ABSTRACT

A measuring device for contactless detection of a ferromagnetic object, comprising at least one magnet; a magnetic field-sensitive element arranged so that an air gap is provided between the magnetic field-sensitive element and the ferromagnetic object; and a soft-magnetic component located between magnet and the magnetic field-sensitive element on a face of the magnet which points in a direction of the ferromagnetic object to be detected, said soft-magnetic component being formed as a cap-shaped element that has a recess that is open in a direction away from said magnetic field-sensitive element to house the magnet and an opening that is open in a direction of the magnetic field-sensitive element, to house the magnet and opening that is open in a direction of the magnetic field-sensitive element, the soft-magnetic component having a first side wall defining said recess and also having a portion which forms a second side wall defining said opening, said first side wall and said second side wall being in alignment with one another.

BACKGROUND OF THE INVENTION

The present invention concerns a measuring device for contactlessdetection of a ferromagnetic object.

Measuring devices of this nature generally comprise an arrangement of amagnet structure and an integrated control circuit chip having a Hallelement, whereby the chip is located on one end of the magnet structureand in the magnetic field that is formed by this magnet structure. TheHall element produces an electrical signal based on the strength of themagnetic field perpendicular to the plane of the Hall element. If aferromagnetic object now approaches the Hall element, the strength ofthe magnetic field perpendicular to the Hall element changes. As aresult, the distance of the ferromagnetic object away from the Hallelement can be represented by an electrical signal produced by the Hallelement. Hall sensors of this type are used to detect rotational speedsor certain positions of toothed trigger wheels (gears) in motorvehicles, e.g., for an antilock braking system or engine management.

For example, to realize a small offset field, measuring devices havingtwo closely adjacent Hall elements were proposed that are interconnectedelectrically in such a fashion that they cancel each other out in thenormal state. This makes it possible to produce a good signal, but thetwo Hall elements must have absolutely identical behavior. This isdifficult to achieve in series production.

Furthermore, a Hall-effect sensor is made known in DE-196 22 561, in thecase of which a Hall element located on a control circuit chip issituated between a trigger wheel and a magnet structure. The magnetstructure is designed so that a north magnetic pole and a south magneticpole are located next to each other and both of them are locatedadjacent to the Hall element.

Furthermore, a magnetic field source is made known in EP-0 273 129, inthe case of which an annular magnet is provided as the permanent magnet.A Hall generator is associated with the opening of the annular magnet insuch a fashion that the axis of the Hall generator and the axis of theannular magnet basically coincide, and, when the magnetic circuit isopen, the Hall generator is located in a space having minimal magneticinduction formed by field displacement within the annular magnet.

SUMMARY OF THE INVENTION

A device, according to the invention, for contactless detection of aferromagnetic object has the advantage, in contrast, that a portion ofthe magnetic flux is shunted away by the soft-magnetic component locatedon one side of a permanent magnet between the permanent magnet and aHall element. The magnetic flux density is therefore reduced in thespace around the soft-magnetic component located on the permanentmagnet. A magnetic circuit having a minimized offset field can berealized as a result in the case of closely adjacent Hall elements, inparticular when measurements are carried out according to thedifferential principle, Hall elements having a relatively largetolerance range can be used, since the different behavior of the Hallelements has a relatively minimal effect. It is furthermore advantageousin terms of the design of the measuring device according to theinvention that, due to the soft-magnetic component located on thepermanent magnet, a strong change in the magnetic flux density occurs inthe presence of a ferromagnetic object. This means that greater accuracyof the measuring device can be obtained by means of the great relativechange in the magnetic flux density that occurs when a ferromagneticobject approaches. The measuring device according to the invention alsohas a simple design, since only one Hall element is required, and thedesign can be realized using a single permanent magnet and asoft-magnetic component having a simple shape. For example, a simplebar-shaped or cylindrical permanent magnet can be used.

The soft-magnetic component is preferably located on a side of thepermanent magnet that faces the direction of the ferromagnetic object tobe detected. A particularly simple design of the measuring device can berealized as a result, since the soft-magnetic component can be easilylocated on a front face of the permanent magnet. As a result, the Hallelement can be easily located in a gap between the soft-magneticcomponent and the ferromagnetic object to be detected.

The soft-magnetic component is preferably formed as a cap-shaped elementand has a recess to house the permanent magnet. As a result, a simpleconnection between the soft-magnetic component and the permanent magnetcan be obtained, e.g., by magnetic forces as well. It is also possible,however, that the soft-magnetic component is interconnected with thepermanent magnet by means of bonding or soldering or welding.

According to a preferred exemplary embodiment, the soft-magneticcomponent has a central opening that is open in the direction of theHall element. As a result, a measuring device can be realized that has aparticularly small offset field.

The soft-magnetic component preferably has a semispherical opening thatis open in the direction of the Hall element. As a result of this, aminimal offset field in particular can be realized when a cylindricalbar magnet is used.

A rotationally symmetrical design is particularly favorable, since thisallows the measuring device to be installed independently of therespective position of the Hall element.

The soft-magnetic component is preferably formed out of a plurality ofannular disks. As a result, a measuring device according to theinvention can be realized using simple components, whereby thecomponents can be standardized and, therefore, different measuringdevices for different requirements can be produced in simple fashion.

According to a preferred embodiment of the present invention, the Hallelement is located between a first permanent magnet and a secondpermanent magnet. The second magnet is situated such that it is locatedbetween the Hall element and the ferromagnetic object to be detected.This arrangement makes it possible to produce a magnetic zero point atthe position of the Hall element. In this fashion, a possibility forperforming equilibration can be realized in particular.

According to a further preferred exemplary embodiment of the measuringdevice according to the invention, the permanent magnet is orientedparallel to the ferromagnetic object to be detected, so that its northmagnetic pole and south magnetic pole lie in a plane perpendicular tothe ferromagnetic object. In this case, the soft-magnetic component islocated on the sides of the front faces of the permanent magnet. TheHall element is located in a gap formed in the soft-magnetic. component.A soft-magnetic component is preferably provided on both front faces ofthe permanent magnet. Due to this design of the soft-magnetic componentsand the arrangement of the permanent magnet in relation to theferromagnetic object to be detected, a relatively large magnetic fieldresults in the Hall element in its sensitive direction without theferromagnetic object being present. If a ferromagnetic object comes intothe vicinity of the permanent magnet, a portion of the magnetic flux isno longer directed through the soft-magnetic component and the Hallelement. Instead, it is directed over the ferromagnetic object. Areduction of the magnetic field in the Hall element is obtained as aresult. In this exemplary embodiment, therefore, the magnetic field inthe Hall element assumes a minimal value when a ferromagnetic objectcomes into the vicinity of the permanent magnet.

BRIEF DESCRIPTION OF THE DRAWINGS

A plurality of exemplary embodiments of the invention are shown in thedrawings and are explained in greater detail in the subsequentdescription.

FIG. 1 is a side view through a measuring device according to a firstexemplary embodiment of the present invention,

FIG. 2 is a top view of a measuring device according to a secondexemplary embodiment of the present invention,

FIG. 3 is a side view through a measuring device according to a thirdexemplary embodiment of the present invention,

FIG. 4 is a side view of a measuring device according to a fourthexemplary embodiment of the present invention,

FIG. 5 is a sectional drawing through a measuring device according to afifth exemplary embodiment of the present invention,

FIG. 5 a is a sectional drawing through a further variant,

FIG. 6 is a sectional drawing through a measuring device according to asixth exemplary embodiment of the present invention,

FIG. 7 is an enlarged partial sectional drawing of the measuring deviceshown in FIG. 6,

FIG. 8 is a sectional drawing through a measuring device according to aseventh exemplary embodiment of the present invention,

FIG. 9 is a sectional drawing through a measuring device according to aneighth exemplary embodiment of the present invention,

FIG. 10 is an illustration of the dependence of magnetic induction onthe width of the air gap in the case of the exemplary embodiment shownin FIG. 9,

FIG. 11 is a sectional drawing through a measuring device according to aninth exemplary embodiment of the present invention,

FIG. 12 is a sectional drawing through a measuring device according to atenth exemplary embodiment of the present invention,

FIG. 13 is a sectional drawing through a measuring device according toan eleventh exemplary embodiment of the present invention,

FIG. 14 illustrates the dependence of magnetic induction on the width ofthe air gap in the case of a measuring device according to the exemplaryembodiment shown in FIG. 13,

FIG. 15 illustrates the dependence of the magnetic fluctuation on thewidth of the air gap of the measuring device shown in FIG. 13,

FIG. 16 is a sectional drawing through a measuring device according to atwelfth exemplary embodiment of the present invention, and

FIG. 17 is an enlarged sectional drawing of the measuring device shownin FIG. 16.

DESCRIPTION OF THE PREFFERED EMBODIMENTS

As shown in FIG. 1, a measuring device 1 according to a first exemplaryembodiment of the present invention comprises a permanent magnet 2 thatis developed as a bar magnet having a diameter d and a height h.Furthermore, the measuring device 1 comprises a Hall element 3 and asoft-magnetic component 7. The soft-magnetic component 7 has acylindrical recess 8 that serves to house the permanent magnet 2. Asshown in FIG. 1, up to one-half of the height h of the permanent magnet2 is covered by the soft-magnetic component 7.

Instead of a Hall element, other magnetic field-sensitive elements canbe used, such as magnetoresistive sensors (anisotropic magnetoresistiveeffect or giant magnetoresistive effect), field plates. Furthermore, aplurality of elements can be used as a differential connection.

As shown in FIG. 1, the Hall element 3 is located in an air gap 6between the soft-magnetic component 7 and a tooth 5 of a trigger wheel 4at a distance a from the tooth 5 and a distance b from the soft-magneticcomponent 7. The distance b should be as small as possible, preferablyzero. The soft-magnetic component 7 extends past the front end of thepermanent magnet 2 by an amount c.

By providing the soft-magnetic component 7 between the Hall element 3and the permanent magnet 2, the measuring device 1 has a magneticcircuit with a very small offset field (a “back bias-reduced magneticcircuit”). The soft-magnetic component 7 acts as the flux concentratingelement that shunts a portion of the magnetic flux away from the frontface of the permanent magnet 2. As a result, the magnetic flux densityin the air gap 6 over the front face of the permanent magnet 2 isreduced, and the Hall element 3 can be located in a region with lowmagnetic induction in the Z direction, i.e., the sensitive axis of theHall element. If a tooth 5 of a trigger wheel 4 is now moved into thevicinity of the Hall element, the magnetic flux is increased in the Zdirection in the Hall element 3, thereby resulting in a higher—in termsof magnitude—Hall voltage. This makes it possible to detect the presenceof a tooth 5 and transmit a corresponding signal to a control device.

The values measured in a comparison of a measuring device with asoft-magnetic component 7 and without a soft-magnetic component arepresented in the following tables 1 and 2. Table 1 lists the measuredvalues for a design corresponding to the measuring device shown in FIG.1. Table 2 lists the measured values for a measuring device without asoft-magnetic component, whereby the design of the measuring deviceotherwise conforms to the device shown in FIG. 1 without a soft-magneticcomponent.

TABLE 1 Measured values with soft-magnetic component 7 Air gap aB_(Z without tooth) B_(Z with tooth) in mm in mT in mT ΔB_(Z) (magn.fluctuation) in mT 0 26.5 55.3 28.8 1.0 26.5 43.0 16.5 2.0 26.5 36.2 9.73.0 26.5 31.9 5.4 4.0 26.5 29.4 2.9 5.0 26.5 28.4 1.9 ΔB_(Z) =B_(z with tooth) − B_(Z without tooth) The permanent magnet is made ofsamarium cobalt. b = 1.5 mm (distance of the front face of the permanentmagnet with a soft-magnetic component away from the Hall element) B_(z):magnetic flux density in Z direction at the location of the Hall element

TABLE 2 Measured values without soft-magnetic component 7 Air gap aB_(Z without tooth) B_(Z with tooth) in mm in mT in mT ΔB_(Z) (magn.fluctuation) in mT 0 22.7 39.8 17.1 1.0 22.7 32.6 9.9 2.0 22.7 28.8 6.13.0 22.7 26.7 4.0 4.0 22.7 25.2 2.5 5.0 22.7 24.5 1.8 The permanentmagnet is made of hard ferrite. b = 2.5 mm (distance of the front faceof the permanent magnet away from the Hall element) B_(Z): magnetic fluxdensity in Z direction at the location of the Hall element ΔB_(Z) =B_(Z with tooth) − B_(Z without tooth)

As demonstrated by a comparison of the measured values in Table 1 andTable 2, the measuring device according to the invention having asoft-magnetic component 3 has a markedly higher change ΔB_(Z) in themagnetic field in the presence of a comparably low offset magnetic field(B_(Z without tooth)=26.5 mT: B_(Z without tooth)=22.7 mT). In fact,ΔB_(Z) with the soft-magnetic component is approximately 35% greater, onaverage, than the value ΔB_(Z) without the soft-magnetic component inthe air gap range of interest of approximately 1 mm to 4 mm. Accordingto the invention, the presence of a ferromagnetic object in the regionof the measuring device can therefore be detected with greater certaintydue to the greater relative change in magnetic induction B, and thedistance of the ferromagnetic object can be determined with greateraccuracy.

FIG. 2 shows a top view of a measuring device according to a secondexemplary embodiment of the present invention. To improve clarity, theHall element is not shown. The measuring device according to the secondexemplary embodiment basically corresponds to the first exemplaryembodiment. The difference is that the measuring device according to thesecond exemplary embodiment has a center through-opening 19 in thesoft-magnetic component 7. As a result, the top region of thesoft-magnetic component 7, i.e., the region directed toward the Hallelement 3, has a cylindrical annular shape.

A measuring device according to a third exemplary embodiment of thepresent invention is shown in the schematic side view of FIG. 3. Thedesign of this measuring device basically corresponds to the measuringdevice shown in FIG. 1. The difference is that the soft-magneticcomponent 7 is designed differently. It has, in addition, longitudinalrecesses 13 on its outer circumferential edge that are formed on theentire circumference of the soft-magnetic component 7. This results inproduction-engineering advantages. By means of this recess, anothermagnetic flux density is obtained in the region of the Hall element 3when a ferromagnetic object or tooth 5 is not present.

FIG. 4 shows a sectional view of a measuring device according to afourth exemplary embodiment of the present invention. In contrast to theexemplary embodiments described previously, the soft-magnetic component7 is not designed as a single component. As shown in FIG. 4, thesoft-magnetic component 7 has a cover 7′ and an annular cylindricalportion 7″ that surrounds a part of the permanent magnet.

FIG. 5 is a schematic sectional drawing of a measuring device 1,according, to the invention, according to a fifth exemplary embodiment.In the case of this exemplary embodiment, the soft-magnetic component 7is designed in such a fashion that, in addition to the recess to housethe permanent magnets 2, it also has a recess 9 with the wall 9 alocated on the front face of the soft-magnetic component 7. As shown inFIG. 5, the Hall element 3 can also be partially located in the recess9. The component 7 can also be composed of a plurality of parts.

In the variant according to FIG. 5 a, the component 7 has a peripheralprojection 20. This projection 20 extends beyond the annular cylindricalportions 7″. In terms of function, the projection 20 corresponds to thewall 9 a in FIG. 5. As a result, magnetic saturation in the edgeregions, i.e., in the region of the transition in component 7 from thefront face to the shell regions, is prevented.

A sixth exemplary embodiment of the measuring device 1 according to theinvention is shown in FIGS. 6 and 7. The difference from the measuringdevice shown in FIG. 5 is that the soft-magnetic component 7 does nothave a recess to house the permanent magnet. Instead, it is locateddirectly on the front face of the permanent magnet 2. The soft-magneticcomponent 7 also has a recess 9 that is open toward the tooth 6, inwhich the Hall element 3 is at least partially located.

FIG. 8 shows a seventh exemplary embodiment of a measuring deviceaccording to the present invention. This exemplary embodiment basicallycorresponds to the exemplary embodiment shown in FIG. 7 with theexception that the recess 9 of the soft-magnetic component 7 is designedsemispherical in shape. Another shape of a recess would also bepossible, e.g., a truncated cone, spherical, conical, etc. It isimportant that a reduction in thickness is obtained in this region. Therecess should be located in the center. Again, the Hall element 3 ispartially located in this recess 9 open toward the air gap 6. In everyexemplary embodiment, the Hall element can also be located over therecess or over the component 7. Furthermore, the soft-magnetic component7 has a recess 8 to partially house the permanent magnet 2.

FIG. 9 is a schematic illustration of a measuring device according to aneighth exemplary embodiment of the present invention. The soft-magneticcomponent 7 is developed out of a plurality of annular disks 7 a and 7b. The annular disk 7 b has a somewhat greater diameter than the annulardisk 7 a so that the Hall element 3 can be adjusted. The height h fromthe top front face of the permanent magnet 2 to the outer surface of theHall element 3 (i.e., to the surface facing the tooth 5) is h=2.5 mm.The diameter of the permanent magnet d was d=7 mm, and the height b ofthe permanent magnet 2 was b=4.0 mm. A Sm₂Co₁₇ permanent magnet wasused. When the measurements were performed, the values for magneticinduction B as a function of the width of the air gap from the outersurface of the Hall element 3 to the surface of the tooth 5 wereobtained. Series 2 shows the values obtained without the tooth 5 beingpresent in the region of the Hall element 3. Series 1 shows the valuesobtained when a tooth was present. As illustrated in FIG. 10, every timea tooth was present in the vicinity of the measuring device, a markedchange in magnetic induction B took place.

FIG. 11 shows a measuring device, according to the invention, accordingto a ninth exemplary embodiment. As shown in FIG. 11, the front face ofthe bar-shaped permanent magnet 2 is not facing in the direction of thetooth 5. Instead, it is arranged with its longitudinal side parallelwith the tooth 5. Two L-shaped, soft-magnetic components 7 a and 7 blocated on the front faces of the permanent magnet 2 in each case at thenorth magnetic pole and the south magnetic pole are provided as thesoft-magnetic component. A gap 11 that is arranged parallel with themagnet 2 is formed between the two legs of the L-shaped, soft-magneticcomponents 7 a and 7 b. A Hall element 3 is located in this gap. If atooth 5 is not located in the vicinity of the permanent magnet 2, alarge magnetic flux travels from the permanent magnet 2 over the firstsoft-magnetic component 7 a, over the gap 11 to the second soft-magneticcomponent 7 b and back to the permanent magnet 2. As a result, highmagnetic induction results in the Hall element 3 when a tooth 5 is notpresent in the region of the permanent magnet 2. If a ferromagnetictooth 5 is now moved into the vicinity of the permanent magnet 2 (referto FIG. 11), at least a portion of the magnetic flux extends over thegap 6 to the tooth 5 and back to the permanent magnet 2. As a result,the magnetic field induced in the Hall element 3 is reduced. In the caseof the ninth exemplary embodiment shown in FIG. 11—in contrast to theexemplary embodiments described previously—the magnetic field in theHall element 3 takes on a minimal value when a tooth 5 is present in theregion of the permanent magnet 2.

FIG. 12 shows a tenth exemplary embodiment of the measuring deviceaccording to the invention. This exemplary embodiment basicallycorresponds to the exemplary embodiment shown in FIG. 11, but thesoft-magnetic element is designed differently. As shown in FIG. 12, thesoft-magnetic element is formed out of an L-shaped, soft-magneticcomponent 7 b and a bar-shaped, soft-magnetic component 7 b. A recess 14is formed in the leg of the soft-magnetic component 7 a, in which saidrecess a Hall element 3 is located. As shown in FIG. 12, in the presentexemplary embodiment, the magnetic flux travels from the permanentmagnet 2 over the soft-magnetic component 7 a, the Hall element 3, overa gap 11 formed between the two soft-magnetic components 7 a and 7 b tothe soft-magnetic component 7 b, and back to the permanent magnet 2.Once more, the soft-magnetic components 7 a and 7 b are located on bothfront faces in each case of the permanent magnet 2, at the northmagnetic pole and the south magnetic pole. The two soft-magneticcomponents 7 a and 7 b are situated on the permanent magnet 2 in such afashion that they partially project into the air gap 6 between thetrigger wheel 4 and the permanent magnet 2 in order to form a recess 9.

An eleventh exemplary embodiment of a measuring device 1 according tothe invention is shown in FIG. 13. As shown in FIG. 13, the measuringdevice 1 comprises a first permanent magnet 2 and a second permanentmagnet 10. A 0.5 mm-thick layer 15, 16 made of magnetically inactivematerial is located on each of the front faces of said second permanentmagnet. Furthermore, a Hall element 3 secured to a printed-circuit boardis provided.

As shown in FIG. 13, the printed-circuit board 12 is secured to asoft-magnetic component 7, so that the soft-magnetic component 7 islocated between the first permanent magnet 2 and the Hall element 3. Thesecond permanent magnet 10 is then located between the Hall element 3and a tooth 5 of a trigger wheel. The following are therefore locatedbetween the permanent magnet 2—made of samarium cobalt, for example—andthe tooth 5, starting at the permanent magnet 2: the soft-magnetic,plate-shaped component 7 having a thickness of approximately 0.2 mm, theprinted-circuit board 12 having a thickness of approximately 1 mm, theHall element 3 having a thickness of approximately 0.7 mm, a first layer15 made of RESITEX having a thickness of approximately 0.5 mm, thesecond permanent magnet having a thickness of approximately 2.5 mm, anda second layer 16 made of RESITEX having a thickness of 0.5 mm.

The magnetic inductions obtained in the Hall element 3 using this designare shown in FIG. 14. The magnetic induction is hereby plotted as afunction of the width b of the air gap 6 between the tooth 5 and thefront face of the magnet structure formed by the layer 16.

In FIG. 15, the magnetic fluctuation in the presence of a ferromagneticobject 5 in the region of the measuring device 1 is shown separatelyonce more as a function of the width b of the air gap 6.

As illustrated in the two graphs in FIGS. 14 and 15, a relatively greatmagnetic fluctuation occurs in the region of the air gap width b between1 and 4 mm in each case that is important for the practical applicationin particular. This magnetic fluctuation occurs in the presence of arelatively small offset field (when a ferromagnetic object is notpresent in the region of measuring device 1) of approximately 17 mT(refer to FIG. 14). The measuring device according to the exemplaryembodiment shown in FIG. 13 therefore represents a Hall sensor having avery low offset field, so that disturbances due to electromagneticincompatibility can be minimized.

In accordance with the variants described previously, the component 7can be developed on the magnet 2, on the magnet 10 or on both.

A twelfth exemplary embodiment according to the present invention isshown in FIGS. 16 and 17. As shown in FIG. 17 in particular, themeasuring device 1 also has a first permanent magnet 2 and a secondpermanent magnet 10. A Hall element 3 and a soft-magnetic component 7are located between the first and second permanent magnets 10. Thesoft-magnetic component 7 is in contact with the first permanent magnet2, while the Hall element 3 is in contact with the second permanentmagnet 10. The two permanent magnets 2 and 10 are arranged in such afashion that their two north magnetic poles face each other on the frontfaces. In accordance with the exemplary embodiment describedhereinabove, an air gap 6 is provided between the second permanentmagnet 10 and a tooth 5 of a trigger wheel. The function of theexemplary embodiment shown in FIGS. 16 and 17 basically corresponds tothat of the eleventh exemplary embodiment shown in FIG. 13, so thatreference can be made to the descriptions there.

In summary, a measuring device 1 for contactless detection of aferromagnetic object 4, 5 was described. The measuring device comprisesa Hall element 3 and at least one permanent magnet 2, whereby amagnetically non-conductive air gap 6 is located between the Hallelement and the permanent magnet. Furthermore, the permanent magnet 2has a soft-magnetic component 7 on at least one of its front faces thatis located in the air gap 6 between the permanent magnet 2 and the Hallelement 3.

The preceding description of the exemplary embodiments according to thepresent invention are intended for purposes of illustration only and notto limit the invention. Various changes and modifications are possiblewithin the framework of the invention without leaving the scope of theinvention or its equivalents.

1. A measuring device for contactless detection of a ferromagneticobject, comprising at least one magnet; a magnetic field-sensitiveelement arranged so that an air gap is provided between the magneticfield-sensitive element and the ferromagnetic object; a soft-magneticcomponent located between the magnet and the magnetic field-sensitiveelement on a face of the magnet which points in a direction of theferromagnetic object to be detected, the soft-magnetic component beingformed as a cap-shaped element that has a recess that is open in adirection away from the magnetic field-sensitive element to house saidmagnet and opening that is open in a direction of the magneticfield-sensitive element, said soft-magnetic component having a firstside wall defining said recess and also having a portion which forms asecond side wall defining the opening, said first side wall and saidsecond side wall being in alignment with one another.
 2. A measuringdevice as defined in claim 1, wherein said opening is formed as a semispherical opening.
 3. A measuring device as defined in claim 1, whereinsaid magnetic field-sensitive element is arranged at least partially insaid opening.
 4. A measuring device as defined in claim 1, wherein saidsoft-magnetic component has a throughgoing opening.
 5. A measuringdevice as defined in claim 1, wherein said soft-magnetic component iscomposed of a plurality of annular discs.
 6. A measuring device forcontactless detection of a ferromagnetic object, comprising at least onemagnet; a magnetic field-sensitive element arranged so that an air gapis provided between said magnetic field-sensitive element and theferromagnetic object; a soft-magnetic component located between saidmagnet and said magnetic field-sensitive element on a face of said manet which points in a direction of the ferromagnetic object to bedetected, said soft-magnetic component being formed as a cap-shapedelement that has a recess that is open in a direction away from saidmagnetic field-sensitive element to house said magnet and opening thatis open in a direction of said magnetic field-sensitive element, saidsoft-magnetic component having a first side wall defining said recessand also having a portion which forms a second side wall defining saidopening, said first side wall and said second side wall being inalignment with one another, wherein a cap of said soft magneticcomponent has an outer circumferential edge provided with longitudinalrecesses in a region of said magnet.